An increase in the demand for biomass for conversion to heat by combustion is likely. The potential role for hemp in supplying this demand is discussed in this article. For hemp, key characteristics such as net calorific value, ash content, and melting behavior, and the risk of corrosion or polluting emissions, are all favorable. Low bulk density and size reduction difficulties might limit its use for pellet production and in small boilers; its use in electricity generating plants and medium-to-large boilers would have better prospects. To mazimize profitability, an agronomy program to achieve high yields at the lowest cost is required. In the Irish climate, this would entail early sowing (late March/early April), a low seed rate (~30kg/ha), and variety selection for maximum stem yields over 10t/ha is attainable. Cost analysis shows that an energy price of about Euros6/GJ is required to achieve a profit level similar to conventional food enterprises. Arable farmers would welcome a break crop in rotation with cereals. Processors needing a year-round fuel supply might be expected to welcome an autumn-harvested crop as part of a mix with spring-harvested crops such as miscanthus and willows. A mix of energy crop species would improve biodiversity and visual impact. Hemp should be a strong contender to be part of the energy crop mix.
The varieties studied were Kompolti, Ferimon, and Fedrina 74. They had stem yields of 12.6t/ha, 11.7 t/ha and 11.6 t/ha respectively. A comparison of the net calorific value of hemp to other cellolusic biomass showed each as follows:
Wood residues 10.0
(the gross values, respectively, were: 18.5, 19.7, 18.0, 21.5).
Bernard Rice is Principal Research Officer, Teagasc, Crops Research Centre, Oak Park, Carlow, Ireland.